Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Reexamination Certificate
2001-04-06
2003-01-07
Tso, Edward H. (Department: 2838)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
Reexamination Certificate
active
06504692
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to the field of arc fault detectors and interrupters, and in particular, to an arc fault interrupter which detects and interrupts upstream and downstream series arcing and downstream parallel arcing, while detecting upstream parallel arcing in order to prevent tripping.
BACKGROUND OF THE INVENTION
A percentage of fires each year are caused by electrical branch circuit wiring arcing faults involving currents below the trip level of a conventional circuit breaker or OCPD (over current protection device) as well as below the handling rate of the breaker. Basic overcurrent protection afforded by circuit breakers is designed to prevent I
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R heating of the wiring in the electrical distribution system, caused by circuit overloading or line-to-line faults, and not necessarily arcing faults. A true short circuit is a rarity in an electrical system. In fact, it is more accurate to think of electrical faults as having some level of impedance, such as a high impedance arc fault (low current) or a low impedance fault (high current). Many electrical faults begin as high impedance breakdowns between the line and neutral conductors or to the ground wire or device components. AFCI (Arc Fault Circuit Interrupter) technology affords protection from conditions that may not necessarily be an immediate threat but could become hazardous if left unattended.
In order to start a fire, three elements must be present fuel, oxygen(air), and energy to ignite the fuel. Arcing is defined as a luminous discharge of electricity across an insulating medium. The electrical discharge of an arc can reach temperatures of several thousand degrees Celsius. Arcing produces sufficient energy to reach the ignition point of nearby combustible material(s) before a circuit breaker can respond. Arc detection is an enhancement to thermal magnetic overload detection typically used in circuit breakers or OCPD's, which alone may not detect and respond to arc faults.
A number of devices for detecting arc faults and methods of detection have been used in the past. These include using E and B field arc sensors, detecting the amplitude of the rate of change of current signals when an arc fault occurs, using non-overlapping band pass filters to detect white noise characteristic of arcs, and utilizing the high frequency components (RF) of arcing waveforms to detect arcing faults. While some of these techniques are more or less effective than others, they require relatively sophisticated arc sensors and circuits. Heretofore, most arc detection circuits have been incorporated in circuit breakers.
“A-type” arc faults are those in which the arc occurs across a break in the line or neutral conductors or at a loose terminal in a branch circuit of a distribution network. The conductors are carrying current to a load derived from the line voltage. The arc could likewise occur as a break or at a loose terminal associated with an extension cord deriving power from line voltage, thereby completing the circuit to the load. Since the current through the A-type fault is limited by the impedance of the load itself, since the fault is in series with the load, an A-type fault is also known as a “series fault.”
B-type” arc faults are a second arcing condition that must be detected and interrupted by a combination outlet device. In a B-type fault, the arc occurs across two conductors in the branch circuit or extension cords plugged into it, at a site where the insulating media separating the two conductors has been compromised. The arc may occur across the line and neutral conductors or the line and ground conductors, or in the case of reverse polarity where the line voltage is reverse-polarized, between the neutral and ground conductors. The current through the B-type fault is not limited by the impedance of the load, but rather by the available current from the supply established by the impedance of the conductors and terminals between the source of line voltage and the position of the parallel fault, i.e., the conductive members carrying the fault current. Since B-type faults are effectively across the line, they are also known as “parallel faults.”
There is a need for simple economical arc fault detectors that can be included in wiring devices such as duplex receptacles, multi-outlet strips, or in-line devices, and that offer the same protection as an arc fault detector incorporated in a circuit breaker but at lower cost. There is a need for an arc fault circuit detector in wiring devices that can be provided at a reduced cost compared with arc fault circuit detecting circuit breakers comparable to the reduction in cost between ground fault interrupting receptacles and ground fault interrupting circuit breakers.
SUMMARY OF THE INVENTION
Briefly stated, downstream series and parallel arcing in AC power lines is determined by using a detector and microprocessor to detect characteristic di/dt behavior received from a current sensor through which the power lines pass. When downstream parallel arcing is detected, the microprocessor uses a speedy algorithm which cannot be used to detect series arcing. Upstream series arcing is detected by sensing a flat voltage portion of the line voltage. Upstream parallel arcing is detected by sensing a voltage spike followed by a voltage flat portion of the line voltage. When upstream parallel arcing is detected, the microprocessor is temporarily shut off to avoid false tripping.
According to an embodiment of the invention, an arc fault circuit interrupter operatively connected between a line side and a load side of an AC electric power distribution system includes first sensing means for sensing a line current in the AC electric power distribution system and producing a di/dt signal; circuit means for processing the di/dt signal and producing an output; tripping means for interrupting power to the load; processing means for processing the output to determine an existence of a downstream arc fault, the processing means including a normal algorithm and a speedy algorithm for processing the output, the processing means sending a trip signal to the tripping means upon determination of the downstream arc fault; second sensing means for sensing a sinusoidal load current of a fundamental frequency of the power distribution system above a first predetermined level; circuit means, responsive to the second sensing means, for initiating the speedy algorithm within the processing means; circuit means for detecting an existence of an upstream series arc, and upon detection of the upstream series arc, for signaling the processing means to send the trip signal to the tripping means; and circuit means for detecting an existence of an upstream parallel arc, and upon detection of the upstream parallel arc, for deactivating the processing means so that the processing means does not send the trip signal to the tripping means.
According to an embodiment of the invention, an arc fault circuit interrupter operatively connected between a line side and a load side of an AC electric power distribution system includes tripping means for interrupting power to the load; first sensing means for sensing upstream arc faults in the AC electric power distribution system and producing an output; processing means for processing the output to determine an existence of a downstream arc fault, the processing means sending a trip signal to the tripping means upon determination of the downstream arc fault; first circuit means for detecting an existence of an upstream series arc, and upon detection of the upstream series arc, for signaling the processing means to trip the tripping means; and second circuit means for detecting an existence of an upstream parallel arc, and upon detection of the upstream parallel arc, for deactivating the processing means so that the processing means does not send the trip signal to the tripping means.
According to an embodiment of the invention, an arc fault circuit interrupter operatively connected between a line side and a load side of an AC electrical power distribution s
Macbeth Bruce F.
Packard Thomas N.
Richards Jeffrey C.
Romano James P.
Pass & Seymour, Inc.
Tso Edward H.
Wall Marjama & Bilinski
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